JPS5835274B2 - Aluminum steel plate - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for controlling an aluminum electrolyzer.

For more details, please refer to the pre-baked aluminum electrolyzer.
It is possible to reliably predict the anodic effect that occurs due to a decrease in the alumina concentration in the electrolytic bath, increase the alumina concentration in the electrolytic bath before the anodic effect occurs, and prevent the anodic effect from occurring. This relates to a method of controlling operation.

To produce aluminum industrially, an aluminum electrolytic bath is used to electrolyze and reduce alumina in an electrolytic bath mainly composed of cryolite.

In normal aluminum electrolyzer operation, the alumina concentration within the electrolytic bath is maintained within the range of about 2-8% by weight.

That is, when the alumina concentration in the electrolytic bath exceeds its saturation concentration (approximately 10%), the alumina in the electrolytic bath is deposited on the upper surface of the cathode, causing so-called bottom fouling.

In an electrolytic cell with fouling at the bottom, the current efficiency decreases significantly.
Furthermore, it takes a long time to recover the normal tank.

On the other hand, when the alumina concentration in the electrolytic bath decreases to 2% or less, a gas film is generated on the bottom surface of the anode in the electrolytic bath, and this gas film increases the resistance between the electrodes, resulting in an increase in the electrolytic voltage. A so-called anodic effect phenomenon occurs, in which the amount of water increases rapidly.

In a battery case in which the anode effect occurs, the electrical voltage in normal operating conditions is approximately 4 to 5 volts, but the electrical voltage is approximately 30 volts, resulting in a large power loss.

The anodic effect is eliminated by supplying alumina to the electrolytic bath and increasing the alumina concentration in the electrolytic bath.

Since the anode effect does not require a long period of time to recover to the normal state of the bath due to bottom fouling, normal electrolytic cell operation is carried out in a low alumina concentration range where there is little risk of alumina deposition, that is, when the alumina concentration in the electrolytic bath is low. It is carried out in the range of 2 to 6%.

As described above, the more the electrolytic cell is operated in a range where the alumina concentration is low, the higher the probability that the anode effect will occur.

Of course, if the anodic effect actually occurs frequently, the current efficiency will deteriorate, so it is possible to predict the occurrence of the anode effect and increase the alumina concentration in the electrolytic bath before the anodic effect occurs, thereby preventing the anodic effect from occurring. We must prevent this as much as possible.

Various methods have been known to predict this anode effect, but the most common method is to measure the electric voltage continuously or intermittently, and to predict the alumina concentration in the electrolytic bath as the alumina concentration decreases. The objective is to predict the anode effect from the increasing electric voltage value.

However, the voltage value rise due to the anode effect occurs within a short time, and the electric voltage value is always 0.01 to 0.0.
Due to the fact that it pulsates around 5V, and that there is a voltage fluctuation of around 0.1 to 0.5V when drawing aluminum metal from inside the electrolytic tank, the anode effect can be affected by the voltage change of the entire electrolytic tank as described above. It is very difficult to predict, and when this method is adopted, it usually requires a complicated arithmetic circuit such as a computer.

Therefore, the present inventors conducted extensive research on a method to easily and reliably predict the occurrence of the anode effect in an aluminum electrolytic cell, and as a result, in a pre-baked aluminum electrolytic cell having multiple anodes, the amount of current flowing through each anode was calculated. The degree of non-uniformity of the amount of current flowing through all the anodes of one electrolytic cell was calculated from these measured values, and the value of this degree of non-uniformity was calculated from 20 to 60 minutes before the anode effect occurred in the electrolytic cell. The present invention was achieved by discovering that the value of the degree of non-uniformity shows an increasing tendency and confirming that by monitoring changes in the value of the degree of non-uniformity, it is possible to reliably predict the occurrence of the anodic effect in an aluminum electrolytic cell. This is what I did.

That is, an object of the present invention is to easily and reliably predict the occurrence of the anode effect in a pre-baked aluminum electrolytic cell, thereby efficiently controlling the operation of the electrolytic cell without causing the anode effect. The purpose of the lever is to continuously or intermittently measure the amount of current flowing through each anode in a pre-baked aluminum electrolytic cell having multiple anodes according to the method of the present invention, and calculate the amount of current flowing through all the anodes by statistical calculation from these measured values. This can be achieved by calculating the non-uniformity of the amount of current flowing, predicting the anode effect based on the value of the degree of non-uniformity, and controlling the alumina concentration in the electrolytic bath.

Next, the present invention will be explained in detail.

Pre-baked aluminum electrolytic cells usually have 1 unit per tank.
It has 0-30 anodes.

The anode is usually manufactured by kneading binder pitch and pitch coke, molding the mixture, and firing the mixture at about 1,100 to 1,300°C.

These anodes gradually wear out during operation of the electrolytic cell, so they must be replaced with new anodes at regular intervals.

In order to avoid a sudden drop in the temperature of the electrolytic bath, these anodes are replaced in units of one or a few of all the anodes, and are sequentially performed every unit time according to the wear of the anodes.

In the present invention, during operation of the electrolytic cell, the amount of current flowing through each of these anodes is measured continuously or intermittently.

To measure the amount of current flowing through each anode, you can attach an ammeter to an appropriate position on each anode conductive rod and directly measure the amount of current flowing through the anode (or anode conductive rod), but instead of measuring the current value, The voltage value may be measured indirectly.

To measure the voltage value, there is a method of measuring the potential difference between two points at any position on the anode conductive rod, a power supply body for supplying current to each anode conductive rod, and a method for fixing the anode conductive rod to the power supply body. The potential difference at any position from the anode conductive rod to the anode is measured by a method of measuring the potential difference with the clamp section of the anode.

However, in this case, the method of measuring the potential difference in each anode conductive rod or the setting method of the voltmeter is necessary so that the potential difference value measured for each anode conductive rod corresponds to the amount of current distributed to each anode. should all be the same.

Next, in the method of the present invention, the degree of non-uniformity of the amount of current flowing through all the anode conductive rods of one battery case is calculated by statistical calculation from the current value or voltage value measured by the above method.

In order to calculate the degree of non-uniformity of the amount of current, known statistical calculation methods such as variance and standard deviation can be used.

For example, the degree of non-uniformity of the amount of current can be calculated by using the following equation (1).

After calculating the value of the degree of non-uniformity, the anode effect occurring in the electrolytic cell is predicted based on the value of the degree of non-uniformity.

The calculated value of the degree of non-uniformity is approximately 6, at which the anode effect occurs.
It gradually increases from 0 minutes before reaching its maximum value when the anode effect occurs.

After this, when the alumina concentration in the electrolytic bath is increased by supplying alumina into the electrolytic bath, the anodic effect subsides, and the value of the degree of non-uniformity also decreases.

Therefore, in the method of the present invention, the simplest method for predicting the anode effect is to continuously or intermittently calculate the amount of current flowing through each anode, which is measured continuously or intermittently. Monitor the degree of non-uniformity at regular intervals,
The previously calculated value of the degree of heterogeneity and the newly calculated value of the degree of heterogeneity are compared, and the temporal change in the degree of heterogeneity shows an increasing tendency, and the difference between the two is as expected. A method is adopted that predicts the anodic effect when the certified value is exceeded.

Alternatively, the value of the degree of non-uniformity calculated continuously or intermittently can be monitored over time, and an anode effect can be predicted when the increase in the degree of non-uniformity with respect to unit time exceeds a set value. Also, if the above method and this method are combined,
Furthermore, the anode effect can be predicted more reliably.

Therefore, in the present invention, the reason why the value of the degree of non-uniformity increases when the anode effect occurs, in other words, the reason why the value of the amount of current flowing through each anode varies depending on the anode when the anode effect occurs is considered to be as follows.

That is, when the anode effect occurs, as described above, a gas film is generated on the bottom surface of the anode, and this gas film becomes the resistance between the electrodes.

However, in the battery case, there are anodes with different bottom shapes depending on the degree of anode wear during electrolysis operation, from a new anode just after replacement to an old anode just before replacement.

When the anode effect occurs, a gas film is likely to be formed on the bottom surface of the new anode because gas is difficult to escape, whereas a gas film is difficult to form on the old anode that has become worn out.

From this, during operation of the electrolyzer, when the anode effect approaches or occurs, it becomes difficult for current to flow to the new anode due to the large gas film resistance at the bottom, while the current flows to the new anode compared to the other anode. Since a large amount of current flows, the value of the amount of current flowing to each anode becomes greatly different, and it is thought that the value of the degree of non-uniformity becomes large.

After predicting the anodic effect based on the value of the degree of non-uniformity in this way, the alumina concentration in the electrolytic bath is increased in order to prevent the anodic effect from occurring.

To increase the alumina concentration in the electrolytic bath, you can crush the alumina solidified bath (crust) on the top of the electrolytic bath and supply it into the bath, or you can insert an alumina supply pipe into the electrolytic bath and supply it. This can be carried out by various known methods, such as a method of directly supplying alumina into an electrolytic bath from a tube.

As described in detail above, according to the method of the present invention, it is possible to easily and reliably predict the occurrence of an anode effect in a pre-baked aluminum electrolytic bath, and to control the alumina concentration in the electrolytic bath before the anode effect occurs. Therefore, it is possible to efficiently control the operation of the electrolytic cell.

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Examples 1 to 2 In two types of pre-baked aluminum electrolytic cells A and B with a sliding current of 135 KA and the number of anodes of 18, voltmeters were attached to all the anode conductive rods of each electrolytic cell in exactly the same way, and the voltage of each anode conductive rod was measured. The potential difference between two points was continuously measured, and the value of the degree of non-uniformity was calculated every 10 minutes from a series of measured voltage values (using equation (1) above).

The calculated values of the degree of nonuniformity are shown in Table 1 and FIG. 1.

From Table 1 and Figure 1, the value of the degree of non-uniformity shows an increasing tendency in electrolytic cell A from 60 minutes before the occurrence of the anode effect, and in electrolytic cell B from 30 minutes before the occurrence of the anode effect. It became clear that the increase in the value of the degree of non-uniformity per unit time (10 minutes) exceeded 0.01 40 minutes before the anode effect occurred, and 10 minutes before the electrolytic cell B. .

Therefore, in electrolytic cells A and B, we continuously measured the potential difference between two points of all anode conductive rods in both cells, and similarly calculated the degree of non-uniformity from the measured voltage values every 10 minutes. The change in the value of the degree of heterogeneity was monitored.

When the amount of increase in the value of the degree of non-uniformity per unit time (10 minutes) in both baths exceeded o and oi, alumina was supplied into the electrolytic bath to increase the alumina concentration in the bath.

Furthermore, when replacing the anode, the amount of increase in the value of the degree of non-uniformity per unit time (10 minutes) exceeded 0.01 before and after replacing the anode, but in this case, alumina was not supplied. Ta.

When the operation of electrolytic cells A and B was controlled for 30 days using the above method, no anode effect or bottom fouling phenomenon occurred during this period, and the operation of the electrolytic cells could be controlled efficiently.

[Brief explanation of drawings]

FIG. 1 is a graph showing temporal changes in the degree of non-uniformity calculated in two types of pre-baked electrolytic cells.

Claims (1)

[Claims] 1. In a pre-baked aluminum electrolytic cell with multiple anodes, the amount of current flowing through each anode is measured continuously or intermittently, and the degree of non-uniformity of the amount of current flowing through all the anodes is determined by statistical calculation from these measured values. A method for controlling an aluminum electrolytic cell, comprising: calculating the degree of non-uniformity, predicting the anode effect based on the value of the degree of non-uniformity, and controlling the alumina concentration in the electrolytic bath.